The embodiment relates to a light emitting device, a light emitting device package, and a lighting system.
A light emitting device (LED) includes a p-n junction diode having a characteristic of converting electric energy into light energy. The p-n junction diode can be formed by combining group III-V elements of the periodic table. The LED can represent various colors by adjusting the compositional ratio of compound semiconductors.
When forward voltage is applied to the LED, electrons of an n layer are combined with holes of a p layer, so that energy corresponding to an energy gap between a conduction band and a valance band may be generated. This energy is realized as heat or light, and the LED emits the energy in the form of light.
A nitride semiconductor represents superior thermal stability and wide band gap energy so that the nitride semiconductor has been spotlighted in the field of optical devices and high-power electronic devices. In particular, blue, green, and UV light emitting devices employing the nitride semiconductor have already been developed and extensively used.
According to a nitride semiconductor LED of the related art, a strain relief layer having an InGaN/GaN layer structure or an InGaN single layer structure is provided under an active layer in order to relieve strain in the active layer.
However, according to the related art, if a lattice matching effect is increased when the strain relief layer having the InGaN/GaN layer structure or the InGaN single layer structure is applied, as the lattice constant of the strain relief layer approximates that of the active layer, even the bandgap energy of the strain relief layer approximates that of the active layer, so that the strain relief layer may absorb light emitted from the active layer.
In addition, although the thickness of the strain relief layer may be increased in order to sufficiently relieve the strain within the limited range according to the related art, operating voltage Vf of the light emitting device may be increased due to the voltage loss in the strain relief layer.